1. Field of the Invention
The present invention relates to an image detection apparatus that generates charges by irradiation with radiation. Particularly, the present invention relates to the structure of a drive circuit substrate of the image detection apparatus and a method for producing the drive circuit substrate.
2. Description of the Related Art
In recent years, FPD's (flat panel detectors), which can directly convert X-ray information into digital data, have become practically used. In the FPD, an X-ray-sensitive layer is formed on a TFT active matrix array. The advantage of the FPD's over conventional imaging plates is that images can be immediately checked in the FPD's. Further, in the FPD's, video images (or motion pictures) as well as still images can be checked. Therefore, the FPD's have rapidly become used by many users.
The image detection apparatus, which is called as FPD, can directly detect image signals. Therefore, it is possible to detect accurate images. However, in some cases, various kinds of noises are added to image signals that should originally be detected.
One of the examples of such noises is a leak current (leak electric current) of a TFT switch. It is desirable that the TFT switch for selecting a detection pixel does not transmit any leak current when the TFT switch is OFF. However, a certain amount of leak current is transmitted due to the characteristic of the device and the transmitted leak current is added to image signals in some cases.
As the material for a photoelectric conversion layer of the image detection apparatus, amorphous Se is used in many cases because amorphous Se has high dark resistance and high response speed. Further, a smoothing layer (interlayer insulation layer) made of an organic material is formed under the amorphous Se layer in many cases. The smoothing layer is formed to smooth a surface on which the amorphous Se layer is deposited (for example, U.S. Pat. No. 6,225,632 and Japanese Patent No. 3589954).
When a photoelectric conversion layer of the image detection apparatus is formed by depositing amorphous Se by evaporation, if the amorphous Se locally crystallizes, a leak current sharply increases in the locally crystallized portion of the amorphous Se. Consequently, it becomes difficult to recognize detection signals, which should originally be detected. In the Se layer that has been deposited by evaporation, crystallization tends to progress especially in an uneven area of the lower layer under the Se layer because crystallization is induced by internal stress generated during vapor deposition.
The structure of an image detection apparatus according to the related art will be described with reference to FIGS. 6 and 7. FIG. 6 is a schematic diagram illustrating a cross-section of the image detection apparatus according to the related art. In FIG. 6, a one-pixel portion of the image detection apparatus according to the related art is illustrated. FIG. 7 is a schematic diagram illustrating a plan view of the image detection apparatus according to the related art. In an image detection apparatus of a direct-conversion type using a layer made of Se or the like as a photoelectric conversion layer 6, it is necessary to place a charge collection electrode 11 between the photoelectric conversion layer 6 and an interlayer insulation layer 12. The charge collection electrode 11 collects charges (electric charges) generated in the photoelectric conversion layer 6. Then, signals are transmitted through a contact hole 16 formed in the interlayer insulation layer 12 and stored in a capacitance between a storage capacitance upper-electrode 13 and a storage capacitance lower-electrode 14 below the interlayer insulation layer 12. Therefore, although the interlayer insulation layer 12 is formed originally to smooth the surface on which the photoelectric conversion layer 6 is deposited, it is necessary to form a contact hole 16 in the interlayer insulation layer 12 at least for each pixel.
The inventors of the present invention have conducted intensive studies and found out that crystallization induced by a height difference of the contact hole 16 (a bent portion of the charge collection electrode 11) tends to frequently occur in a portion of the photoelectric conversion layer 6, the portion on the upper side of the contact hole 16. If such crystallization occurs, a leak current of Se increases in some specific pixels. Consequently, the leak current increases and affects data of other pixels. Hence, it becomes difficult to recognize detection signals, which should originally be detected.